Fluid pressure connector for printed circuit card



April 4, 1961 J. E. MCGREGOR 2,978,666

FLUID PRESSURE CONNECTOR FOR PRINTED CIRCUIT CARD Filed May 27, 1957 IN V EN TOR. A JOHN E. M mama United States Patent FLUID PRESSURE CONNECTOR FOR PRINTED CIRCUIT CARD John E. McGregor, Poughkeepsie, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed May 27, 1951, Ser. No. 661,803 4 Claims. cl. 3395 17 tween the individual contact members is determined by the spring rate or tension of the contact. While such connectors may be suitable for circuits wherein relatively wide variation of. contact resistance between the individual contact members can be tolerated, such connectors will not function in high speed low power applications. Due to the inherent ditficulty in maintaining uniform tension and mechanical tolerances between the individual contacts in the prior art connector assemblies, the contact resistance between individual contacts of the'connector tend to fluctuate over a relatively wide range with respect to each other. Generally speaking, the electrical resistance of contacts in a connector will vary as a function of the pressure maintained between the individual'contactmembers. However, the maximum pressure which can be applied to the contacts in conventional connectors is limited by the insertion and removal force required to insert and remove the male member of the connector without deformation of the contacts.' When the contact pressure is increased abovea particular limit, continued use results in contact fiexure as well as deformation of theassociated contacts. Such deformation and relative motion may result in removal of the contact protective coating, making a firm low resistance contact impossible and causing the resultant contact resistance to be both higher and of inconsistent value. I I

In addition to the above described limitations, any vibration resulting from mounting on an applied shock will increase the normal variation of contact resistance of the individual contacts.

Another method employed in the prior art for providing a relatively high contact pressure between cont-act members utilizes a cam or eccentrically mounted roller.

However, the close tolerances required for machining cams and the difliculty resulting from angular displacement of cam members or cam-member wear limits the utility of this approach. In addition, it is difficult to maintain uniform contact pressure between the individual contacts in a multi-contact assembly.

From the above description, the need for a connector having uniformly lowcontact resistance between the individual contacts as well as low insertion and removal force is apparent.

The present invention is directed to a multiple contact connector wherein each contact member comprises a pair of opposing contacts suitably insulated from adjacent contacts and indexed in position in the assembly by separators. The plug in a preferred embodiment is in the form of a printed circuit card havinga plurality of conductor strips corresponding to the'position of the contacts within the assembly. A'pressure responsiveflexible member is applied pressure to constrain the contacts against the conductor strips, thereby providing low and substantially uniform resistancebetween the individual contacts within the assembly. The contacts are so adjusted as to provide either zero or a nominal insertion and removal force sufficient to remove oxidation of the contacts by a wiping.

action. To remove the plug after insertion, the pressure is removed whereby the resulting collapse of the flexible member permits the contacts to return to their previous position.

- Accordingly, a primary object of the present invention 1s to provide an improved electrical connector..

Another object of the present invention is to provide 7 a pressure controlled connector for maintaining uniform contact pressure between the individual contact members.

Another object of the present invention is to provide a pneumatically or hydraulically controlled connector for maintaining uniform contact pressure between the individual contact members.

Still another object of the present invention is to pro:

videan improved multiple contact connector assembly .having a low insertion and removal resistance and adaptedto provide a uniform contact resistancebetween the individual contacts of the assembly.

Another object of the present invention is to provide an improved pluggable unit assembly comprising a connector and printed circuit card adapted to provide low asspciated with each contact expands inresponse to I and uniform contact resistance between the contact members of a connector and the conductor strips of the printed circuit card.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by Way of example, the principle of the invention and the best mode which has been contemplated ofapplying that principle In the drawings:

Fig. I is an exploded drawing of the connector assembly comprising a connector and pluggable unit card.

Fig. 2 is a cross section on line 2-2 of Fig. l illustrating an individual contact assembly within the con nector.

Fig. 3 is a front elevation view of the connector assembly with parts of the structure broken away to illus' trate the inner construction thereof.

Referring now to the drawings and more particularly to Fig. 1 thereof, the connector comprises a plastic retaining shell or chamber 21 having a recessed portion 23 containing a contact assembly consisting of a plurality of contacts 25, plastic separators 27, end portions 29, 30 and plastic tubing 31. The retaining shell may be considered as the female section of a connector assembly into which the male section in the form of a printed circuit card 35 is inserted.

The contact assembly, as described hereinafter, includes a plurality of contacts, each contact having a configuration of a double open-sided loop assembly through which a single plastic tube is threaded. The re- .27. Whilethe preferred embodiment of the connector contains a total of 10 contacts, the number of contacts in the arrangement is optional and will correspond to the requirements of the individual circuit. The contact member-s25 constructed in accordance with the present invention comprise a pair of cooperatively opposed female contact members consisting of relatively thin strips of electrically conductive material such as Phosphor-bronze. The contact members are in the form of open loop members such as 3-9 and 41 which are integral with a base member or prong but separated from each other by a distance corresponding approximately to the width of the conductors of the printed circuit card 35.

Plastic spacers 27 are formed with recesses 43 and 45 on each side of a center portion 47, the recesses corresponding to the shape of the open loop contact members and adapted to guide the contacts securely in position. Thus, as shown in detail in Fig. 3, the depth of the recesses in the spacers corresponds to substantially half the width of the contact members whereby each spacer is capable of receiving half of two contacts on either side thereof while two inserts are required to completely enclose a single contact. In addition to insulating the contacts from each other, the spacers may serve also as means for indexing the contacts in their proper position with reference to conductor strips 49 of printed circuit card 35. Each of end pieces 29 is also indented to contain half of the adjacent contact in a manner similar to the spacers.

To assemble the subject device, two alternative methods are possible. Assuming that the channel or shell 21 is fabricated as a single piece, an end member such as member 30 could be inserted within the shell and secured in position by its associated pin 37. The plastic tubing after being looped through end member 29, is inserted through the holes in end piece 30 either prior or subsequent to afiixing the end piece in position. A first contact element of contact members 25 could then be threaded about the tube, the prong of the cont-act passed through the bottom of the contact recess and the contact slipped into position. Separators and contact elements would be alternately inserted in the manner described until the contact assembly has been completed. Slipping the contacts and separators into position may be facilitated by pulling the open ends of tubing 31 as each component is threaded thereon. After the inner contact assembly has been completed, end member 29 could be inserted and secured by pin 37.

An alternative method of assembly would require fabrication of the channel or shell in two identical pieces, along the axis identified as line 51. The entire inner contact assembly comprising contacts, spacers and tubing could be assembled, inserted within the shell and the two sections of the shell joined to form a single structure. The two halves could be joined in a conventional manner by means of a thermo-setting plastic or glue.

The male portion of the connector in the preferred embodiment comprises a printed circuit card 35 having land portions or conductor strips 49 suitably spaced to correspond to the position of contacts 25 in the contact assembly. In the ensuing description of the operation of the subject device, reference should be made to Figs. 2 and 3 which illustrate details of the connector assembly. The printed circuit card 35 having land areas 49 is initially inserted in the opening 23 of the connector, the opening of the connector being of sudh a size as to exert zero or a nominal insertion resistance to the printed circuit card. In the preferred embodiment, the contacts are adjusted to provide a wiping action upon insertion and removal of the printed card to prevent or remove metal oxides. To provide contact between the contact 25 .and the associated conductor strips 49 on both sides of the printed card, a closed pneumatic loop could be provided by applying air pressure from an air pressure tank to one end of the flexible tubing 31 and sealing the other end of the tubing. Upon applying suflicient pressure to the tubing, the flexible tube expands thereby constraining the multiple contacts against the corresponding conductor stripsv of the printed card thereby affording a low and substantially uniform contact resistance.

The constraint between the connector contacts and printed card is sufficient to compensate for any normal variation in contact resistance and to provide a low and substantially uniform resistance between the contacts and their associated conductor strips. The resulting pressure exerted on the individual contacts is uniform and substantially independent of the resiliency of the contact members. In a particular model constructed, the contact loops made of beryllium copper and the conductor strips on the printed circuit card made of lead-tin provided uniform contact resistance and low electrical resistance. In another model having gold plated beryllium cont-acts employed to check the variation in contact resistance with variations in pressure, the contact resistance initially decreased as the air pressure increased but tended to stabilize when the air pressure reached a nominal value of approximately 12 psi. Little variation in contact resistance was noted within a pressure range of 12 to 28 p.s.i.

To remove the printed circuit card from the connector, the fluid pressure is eliminated or substantially reduced thereby restoring the contacts to their normal position and permitting removal of the printed card with a nominal removal force. Alternatively, a vacuum might be applied to cause the flexible tubing to collapse. In this manner, low insertion and removal forces and a reliable uniform contact between the individual contact members are provided. While a pneumatically operated arrangement has been described in the preferred embodiment, it will be apparent to one skilled in the art that a hydraulically actuated arrangement may be employed.

Referring briefly to Fig. 2, there is illustrated a side view of the connector assembly in the actuated condition. As shown therein, the circuit card 35 rests on the lower curved portion of the plastic spacer 27. When the plastic tubing is expanded, the inner surfaces of contact loops are forced against the associated conductor strips of printed circuit card 25. To remove the printed circuit card from the contact recess of the connector, the fluid pressure will be removed or substantially reduced to permit the plastic tubing to become unflexed and thereby reduce the contact pressure between the contact surfaces and card to a level such as to require minimum removal force. Thus the printed circuit card can be readily inserted in the connector without scoring the conductor strips of the card or causing excessive wear on the associated contact members. In this manner, the desirable and heretofore conflicting characteristics, of low insertion and removal force and low contact resistance between the contacts and conductor strips on the printed circuit are attained. The printed circuit card may have flanges, the upper surface of which may rest on the end members of the connector. For example, the upper surface of flanges 53 and55 may rest on the corresponding edge of end members 31 and 33 respectively. In addition, if desired, the assembly could obviously be polarized by use of a key on the socket and an open key slot on the printed circuit card.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is: I

1. A multiple contact connector assembly for providing low and substantially uniform contact resistance between the individual contacts of said assembly and conductor strips on a printed circuit card comprising a recessed body portion of insulating material, a plurality of contact members within said recess, each contact member comprising a pair of opposed open loop finger members connected to a common-terminal,- a plurality of spacers mounted between adjacent contact members, said spacers having recessed portions on each end thereof adapted to position and contain the finger members of adjacent contacts, first and second end portions, each end portion being recessed to retain a portion of the adjacent contact in position, a tubing member threaded through said contacts and end portions of said assembly, said tubing member responsive to air pressure applied thereto to expand, thereby causing said contact members to press against the adjacent conductor strips of said printed circuit card.

2. A pressure actuated electrical connector assembly comprising in combination a printed circuit board having a plurality of parallel spaced conductor strips thereon, asocket member comprising a recessed body portion of insulating material, a plurality of contact members corresponding in number and position to the conductor strips on said printed circuit card within said recess, each of said contact members including a pair of opposed finger members electrically common, a section of tubing, said tub ing being threaded through each of said contact members and means for applying fluid pressure to said tubing whereby the resultant expansion of said tubing forces said contact members against the adjacent conductor strips on said printed circuit board to thereby provide low and substantially uniform contact resistance between said contacts and said conductor strips.

3. An electrical assembly for supporting a printed circuit card and providing low resistance connection between contacts of said assembly and conductor strips in said printed circuit card comprising a socket member of insulating material having a recessed portion therein, a contact assembly positioned within said recessed portion, said contact assembly comprising a plurality of contacts, each of said contacts having a pair of opposed contact fingers in wiping relationship with said conductor strips during insertion of said printed circuit card, and expansible means having a single pressure fluid cavity, said expansible means being disposed in proximity to all of said plurality of contacts so as to constrain said contacts against the conductor strips of said printed circuit card when the pressure in said pressure fluid cavity is increased.

4. A connector assembly for providing uniform resistance between a plurality of contacts and corresponding conductor strips on a printed circuit card, comprising a body of insulating material having an inner recessed portion, a contact assembly mounted within said recessed portion, said contact assembly comprising a plurality of contacts, each of said contacts including a pair of opposed finger members, means for securing said contact assembly within said recessed portion, and an expansible member having a single pressure fluid cavity, said expansible member being adapted to force all of said finger members into contact with their associated conductor strips upon expansion of the expansible member by fluid pressure.

References Cited in the file of this patent UNITED STATES PATENTS 2,456,902 Treuthart Dec. 21, 1948 2,494,244 Jonard et al Jan. 10, 1950 2,654,872 Saul et a1. Oct. 6, 1953 2,685,071 McCreary July 27, 1954 2,711,523 Willis June 21, 1955 2,802,188 Badders Aug. 6, 1957 2,811,700 Kuch Oct. 29, 1957 2,825,037 French Feb. 25, 1958 2,857,577 Vanderpool Oct. 21, 1958 

